1. Field of the Invention
This invention relates to a process for retorting raw shale comprising the following steps:
(1) passing raw shale downwardly through the upper zone of a two-zoned vertical retort; PA0 (2) introducing a gas comprising molecular oxygen and flue gas at a temperature of about 590.degree. to about 760.degree. C., and ambient pressure into said upper zone and passing the same upwardly through said upper zone in contact with said raw shale; PA0 (3) recovering from an upper part of said upper zone a product comprising shale oil and retort gas; PA0 (4) passing the treated shale from a lower part of said upper zone downwardly through the lower zone of said two-zoned retort; PA0 (5) introducing molecular oxygen at a temperature of about 25.degree. to about 100.degree. C. and flue gas at a temperature of about 25.degree. to about 200.degree. C., and ambient pressure into said lower zone and passing the same upwardly through said lower zone in contact with said treated shale; PA0 (6) recovering from an upper part of said lower zone a preheated gas comprising molecular oxygen and preheated flue gas; and PA0 (7) recovering from a lower part of said lower zone spent shale. PA0 (1) passing raw shale downwardly through the upper zone of a two-zoned vertical retort; PA0 (2) introducing a gas comprising molecular oxygen and flue gas at a temperature of about 590.degree. to about 760.degree. C., and ambient pressure into said upper zone and passing the same upwardly through said upper zone in contact with said raw shale; PA0 (3) recovering from an upper part of said upper zone a product comprising shale oil and retort gas; PA0 (4) passing the treated shale from a lower part of said upper zone downwardly through the lower zone of said two-zoned retort; PA0 (5) introducing molecular oxygen at a temperature of about 25.degree. to about 100.degree. C. and flue gas at a temperature of about 25.degree. to about 200.degree. C., and ambient pressure into said lower zone and passing the same upwardly through said lower zone in contact with said treated shale; PA0 (6) recovering from an upper part of said lower zone a preheated gas comprising molecular oxygen and preheated flue gas; and PA0 (7) recovering from a lower part of said lower zone spent shale;
2. Description of the Prior Art
Unlike the invention herein, U.S. Pat. No. 2,774,726 to Eichna discloses a vertical shaft retort with complex internal structures. Raw shale enters a separate preheating zone into which non-combustion supporting gas at an elevated temperature has been injected. The non-combustion supporting gas is derived from gases leaving the combustion zone, recycle gas from the preheating zone, recycle product gas and air. The preheated shale enters a retort zone in which the shale is heated from exiting combustion gas. Shale from the retort zone flows into a combustion zone where it is burned in contact with a mixture of air and recycle gas from the preheating zone. Eichna differs from the invention herein in that the present invention has a two-zoned retort with the two zones being maintained by means of a substantially zero pressure differential across a section of the retort. As a result of maintaining such differential pressure, oxidizing gases can be handled in the lower zone and reducing gases in the upper zone. This concept is not disclosed by Eichna. Furthermore, the gas flow rates in the two zones of the retort in the present invention are different and are independently controlled. Finally, the preheated oxidizing gas injected to the lower part of the upper zone of the retort herein is for combustion and retorting, whereas the gas of Eichna is non-combustion supporting at low temperature for preheating shale and not for combustion and retorting.
U.S. Pat. No. 3,318,798 to Kondis discloses a vertical shaft retort which incorporates external combustion of recycled product gas and injection of the hot gas to the combustion zone of the retort. Kondis discloses a gas combustion retort that does not contain separate zones in which different gas streams which are independently varied flow. Further, cooling of shale is accomplished by recycling product gas and not by cooled flue gas. Cleanup of flue gas is not covered.
U.S. Pat. No. 3,573,194 to Hopper discloses a vertical retort in which the various steps of the process are contained in separate vessels, i.e., a preheating vessel, a retorting vessel, a combustion vessel, and a cooling vessel, arranged vertically. The objective of the Hopper disclosure is to retort at elevated pressure using inert gas, such as nitrogen and carbon dioxide, to obtain a shale oil of improved product quality. The steps of preheating, combustion, and cooling are accomplished at atmospheric or low pressure; however, the retorting step is at elevated pressures. Heat for retorting is supplied by gases from the combustion step, externally heated recycle product gas and externally derived inert gas. The invention herein is designed to provide an upper zone of a retort having carefully controlled maximum temperatures to decrease the possibility of slagging, agglomeration, and bridging within the retort. In the lower zone of the retort herein, sensible heat is recovered from retorted shale and is preferably injected to an external furnace, heater or boiler for heat recovery rather than to transfer that heat upward in the retort to the upper zone as is done in other retorts. As a result, the lower zone of the retort herein is also used for removal of sulfur oxides from flue gases, reduction of nitrogen oxides, and for recarbonation of decomposed mineral carbonates. In addition, combustion product gas which is evolved and heat of combustion which is generated in the lower zone can be transferred to an external furnace, heater or boiler.
Although the invention herein is effective for use with rich grades of shale feeds it is especially suitable for use with lean grades of shale which are not economically feasible for processing in conventional retorts.